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From: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: Comparing numbers and regular expressions
Message-ID: <11278@jpl-devvax.JPL.NASA.GOV>
Date: 2 Feb 91 01:11:57 GMT
References: <5152@s3.ireq.hydro.qc.ca>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 41

In article <5152@s3.ireq.hydro.qc.ca> gamin@ireq-robot.hydro.qc.ca (Martin Boyer) writes:
: 
: I'm trying to compare a numeric user id against a list of numbers.
: Here's my attempt; it doesn't work, possibly because the regular
: expression search doesn't treat the numbers as strings:
: 
: $uid_list = "13|1";
: 
: $this_uid = 101;
: 
: if ($this_uid =~ /^$uid_list$/o) {
:     print "Matches!\n";
: } else {
:     print "Doesn't match.\n";
: }
: 
: This section prints Matches!, but that's not what I want; what I want
: is for the test to succeed only for values of 13 or 1.

Well, look at the pattern you're actually searching for: /^13|1$/
Note that ^ and $ don't automatically distribute over alternatives.
/1$/ matches 101.

You want /^(13|1)$/.  So say /^($uid_list)$/ and it should work.

Note that this is essentially a linear search.  If you're doing lots of
comparisons against a longish list, it'll be much faster to load up
an array to check with:

    for (split(/\|/, $uid_list)) {		# or equivalent
	$valid_uid[$_] = 1;
    }
    ...
    if ($valid_uid[$this_uid]) { ...

If your uids get too large to use a normal array, use an associative array
instead.  A vec() would also work, and save a lot of space over a normal array:

    if (vec($valid_uid, $this_uid, 1)) { ...

Larry